An effective push fastener is disclosed in U.S. Pat. Nos. 2,995,969 and 3,125,922. This type of fastener is both secured and released by axial movement of a plunger, and requires no tools for its operation. Included in the fastener is a plunger having a shoulder at one end that is engaged and retained by two opposed inwardly directed leaf spring elements. These leaf spring elements are held to one of the members to be secured while the plunger is carried by a housing on the other member to be secured and is biased in one direction by a compression spring. The plunger includes a second shoulder that is engageable with a release element in the form of a disc slidable on the plunger between the two shoulders. Inward movement of the plunger moves the release disc outwardly to engage the leaf spring elements, forcing their outer ends apart and away from the plunger so that they no longer hold the plunger. The releasing disc is frictionally retained by the opposed leaf springs until the plunger is moved inwardly by the compression spring to a released position.
Although this is a very satisfactory fastener in most respects, it poses certain difficulties in manufacture and under some circumstances can cause trouble in service. It is necessary that the opposed leaf spring elements be precisely aligned and positioned for proper retention of the plunger when the fastener is in the mated condition. If they are bent out of alignment, their retention force becomes reduced. Moreover, if the leaf springs are misaligned, the release disc may be unable to deflect the outer ends apart sufficiently to release the shoulder on the plunger from the leaf springs. In that event, the fastener cannot be separated. It is quite difficult to manufacture the leaf spring elements to the necessary degree of accuracy and a substantial amount of hand work has been necessary in producing these fasteners. This slows down production and adds to the cost. Also, the spring elements, projecting from the workpiece when the fastener is in service, are vulnerable and relatively easily bent to a misaligned condition. In addition, by including only two spring prongs to support the load imposed on the fastener, its load carrying capacity has been limited.